The present invention relates to a process for preparing explosive, propellant and pyrotechnic compositions, and generally black powder and black powder substitute. More specifically, the present invention relates to a process for preparing a black powder substitute in which an alkali metal nitrate, sulfur and at least one organic fuel are effectively combined in an extruder. The process preferably avoids lacquering and is preferably essentially binder-free.
Black powder is one of the oldest energetic materials known to mankind. Over the centuries, this energetic material has been used in industrial, entertainment, and military applications. During this time the fundamental formulation has not varied in substantial part. Historically, this low explosive composition has been composed of potassium nitrate or sodium nitrate, charcoal and sulfur. Despite the ready knowledge of the basic ingredients in its formulation, manufacture of black powder has remained more an art than science.
Slight differences in the ingredients lead to widely varying and unpredictable energetic performance. For instance, historically, problems have arisen resulting from slight change made in the production of charcoal slated for use in black powder manufacture. Charcoal is produced by carbonization of wood which is a natural product that has physical and chemical properties which are a function of tree species, soil composition, and other variables. Due to these and other variables, the properties of charcoal, such as its composition, ash content, pore structure, and density, will not be uniform during production, and that causes variable performance of black powder.
Efforts to avoid this and other problems include searches for substitutes for black powder. Among the proposed alternatives to carbon include specified crystalline organic compounds as disclosed in U.S. Statutory Invention Record No. H72 (Jun. 3, 1986), the complete disclosure of which is incorporated herein by reference. Although a diverse number of replacements have been proffered, none have proven to be a general substitute. Some proposed compositions exhibit satisfactory performance in limited special applications, whereas others lack the desired consistency in performance to fulfill requirements. Still others offer an apparent performance match in confined conditions, but burn poorly under less confined conditions.
Thus, in practice the presently known practiced batch process for making black powder is as shown, in part, in FIG. 1. It can be generally characterized by an essential first step which involves ball milling sulfur and charcoal to obtain an intimate mixture of the two ingredients. This first step is an essential one. Simple mixtures of the three known main constituents of black powder do not perform satisfactorily. A second step involves rod milling the potassium nitrate. The third step comprises the muller operation. The third step uses a unique muller design in which the muller is floated on bed of melted and solidified sulfur. The sides of the muller are wooden and the steel wheels of the muller weigh about 10 tons each. A materials charge comprised of potassium nitrate, sulfur, and charcoal is placed in the muller and a small but effective amount of water is added as a processing aid. The mixture is mulled until the consistency is visually determined to be correct. Mulling usually requires 4 to 5 hours. After mulling, the mulled material has a water content of about 3 percent. The a fourth step comprises shoveling the mulled mixture into a cart for transfer to the blocking building. The fifth step comprises block pressing the mulled mixture. The block press is a long wooden trough with aluminum plates spaced apart at intervals of about 4 inches. The block press is filled with the mulled mixture. A hydraulic press compresses the powder in the block press into black powder blocks about 1 inch thick and two feet square. A sixth step requires manually removing the black powder blocks and using a coarse toothed crusher to break the blocks into chunks for subsequent treatment in a corning mill. In,the seventh step the corning mill breaks the chunk into coarse particles which are then screened into various granulations. In a seventh step, most of the black powder is used to prepare 5000 pound batches of graphite glazed black powder in a rotating wooden barrel. The resultant finished product is typically packed 10 and packaging is generally in the form of 25 pound steel cans provided with a plastic liner and thereafter stored in magazines prior to shipment.
The presently practiced manufacturing process presents a number of drawbacks. The process is labor intensive and potentially dangerous due to the equipment being operated.
More recent attempts to develop alternative methods for making black powder and black powder substitutes are disclosed in Proceedings of the Eighteenth International Pyrotechnics Seminar, pages 925-938 (Jul. 13-18, 1992); U.S. Pat. Nosw. 5,320,691 and 5,425,310, the complete disclosures of which are incorporated herein by reference. In a disclosed method, potassium nitrate, sulfur and phenolphthalein are combined together with an alcoholic potassium hydroxide and water, mixed and alcohol evaporated off, granulated, dried-and collected. These methods have shown promise, but have not proven entirely satisfactory. Corrosion of mixing equipment and evolution of organic volatile materials during mixing are among the added difficulties with these methods.
Accordingly, a need for a less labor intensive and simpler process for making black powder and black powder substitutes remains unfulfilled.
The present process avoids organic volatiles while preparing an intimate mixture of the essential ingredients of black powder or, in particular, a black powder substitute.
The present process is less labor intensive than the presently commercially practiced process for the preparation of black powder and substitutes.
The present process can be remote operated and/or monitored.
The present process avoids, if not at least substantially reduces, the corrosion problem noted with some proposed alternatives to the present commercial process.
The present process can be practiced on a continuous basis.
These and other objects are achieved by the present invention.
According to the present invention, a black powder substitute is obtainable by preparing a salt of a multi-ring organic compound as a substitute for charcoal, preparing an intimate admixture of the thus produced salt and sulfur within a targeted weight (or molar) ratio of these ingredients, particulating the oxidizer sufficiently to permit its blending with, the salt and sulfur, extruding these ingredients in the presence of water (up to about 10 weight percent) and a small but, effective amount of slickening agent, e.g., water soluble polymer, preparing tan extrudate of pre-selectable geometry, cutting the extrudate to a desired size and configuration, optionally drying the cut extrudate, optionally subjecting the cut extrudate to a rounding treatment, and packaging and storing the cut extrudate for subsequent use or shipment. The extrusion step can be characterized as being conducted essentially free of alcohol, and specifically at least essentially free of an alcoholic potassium hydroxide solution. As a consequence, when conducted the extrusion step is in general essentially free of VOC emissions. In the present process, different agents and additives can, if desired, be introduced, such as agents for reducing the electrostatic sensitivity (ESD) at different steps.